Although we’ve seen this sort of thing a few times before, the news yesterday that researchers in Cambodia detected two patients with dual influenza infections (back in 2009) has made quite a splash in the media overnight.
Some of the headlines include:
Cambodians infected with both swine, seasonal flu The Straits Times
Like the influenza virus itself, the UK papers tend to go for the throat with their headlines:
Britain On Alert For New Super-flu Daily and Sunday Express
Before these hyperbolic headlines entice anyone to head down to the bunker, the study on which these stories are based found no `super flu’.
In fact, while researchers detected a relatively rare dual infection of seasonal H3N2 and the new pandemic H1N1 virus in a pair of Cambodian patients, in neither case did they find a reassortant virus.
The point is, this is the sort of set up that could have produced a new, potentially dangerous hybrid virus.
First stop, the study which appears in the American Journal of Tropical Medicine & Hygiene, then we’ll come back and look at the potential ramifications of dual influenza infections.
Christopher A. Myers, Matthew R. Kasper, Chadwick Y. Yasuda, Chin Savuth, David J. Spiro, Rebecca Halpin, Dennis J. Faix, Robert Coon, Shannon D. Putnam, Thomas F. Wierzba and Patrick J. Blair
The details are behind a pay wall, but as the authors point out in their abstract:
This incident confirms dual influenza virus infections and highlights the risk of zoonotic and seasonal influenza viruses to coinfect and possibly, reassort where they cocirculate.
Earlier this year you may recall we saw a similar co-infection in Canada that actually led to the creation of a unique hybrid reassorted virus (see Webinar: pH1N1 – H3N2 A Novel Influenza Reassortment).
In this case, the patient was a 16-month old boy from the Greater Toronto Area who was admitted briefly to a local hospital for respiratory and gastrointestinal symptoms in January of 2011.
The child was sent home, and recovered without incident, and no other family members or contacts reported flu-like symptoms.
It wasn’t until later, when viral cultures showed a hybrid (reassorted) H1N1-H3N2 virus, did scientists realize that something unusual had occurred.
Details of this event were presented in an online webinar on June 16th of this year.
From the abstract:
Dr. Jonathan Gubbay- Medical Microbiologist, OAHPP
Dr. Jonathan Gubbay, medical microbiologist at the Toronto Public Health Laboratory, will present on a new influenza virus that has been discovered by the Ontario Agency for Health Protection and Promotion (OAHPP). It is the first Canadian confirmed finding of a patient with a coinfection of seasonal H3N2 and pH1N1 followed by reassortment.
A little more than a year ago, in EID Journal: Co-Infection By Influenza Strains, I wrote about a study in New Zealand during the opening months of the 2009 pandemic that discovered at least 11 co-infections (out of 1,044 samples tested) with the older seasonal H1N1 virus and the newly emergent pandemic H1N1 virus.
Matthew Peacey , Richard J. Hall, Stephanie Sonnberg, Mariette Ducatez, Shevaun Paine, Mackenzie Nicol, Jacqui C. Ralston, Don Bandaranayake, Virginia Hope, Richard J. Webby, and Sue Huang
The authors state that the rate of co-infection could actually be higher, since samples were not checked for any other flu strains such as H3N2 and influenza B.
And going back even further, Maryn McKenna wrote – in an article for CIDRAP News – of an Indonesian teen who was found to have been co-infected with an avian (H5N1) and a human (H3N2) influenza strain.
Maryn McKenna Contributing Writer
Mar 17, 2008 – ATLANTA (CIDRAP News) – An Indonesian teenager has been brought forward as a case of simultaneous infection with seasonal and avian strains of influenza—a possibility that health planners have long warned could give rise to a pandemic flu strain.
In the Indonesian and New Zealand cases above, no reassortant viruses were detected. Still, this research suggests that humans, like swine, could be `mixing vessels’ for influenza.
While gene swapping is possible under a co-infection scenario, it isn’t by any means assured.
And even should a reassortment take place, the resulting virus might not prove biologically `fit’, or if it is `fit’, any worse than either of its parental strains.
However, the potential for creating a devastating novel flu strain cannot be discounted.
Last August, in Professor Peter Doherty On Bird Flu, we looked at his worries on the possibility that the H5N1 virus might one day swap genes (reassort) with the H1N1 virus and produce an easily transmitted, highly virulent flu strain.
And in September we saw research (see Study: Reassorted H1N1-H5N1 Produced Virulent Strain) where a laboratory-created reassortant virus with genes taken from the H5N1 and H1N1 virus produced a highly transmissible and virulent strain.
Of course, while the world was waiting for bird flu, in 2009 a reassorted Swine flu virus unexpectedly sparked a global pandemic. We were fortunate that it wasn’t any more severe than it was, but it illustrates that there are many ways a pandemic can evolve.
In addition to the various clades of human flu strains ( both pdmH1N1 & H3N2) now circulating, and a growing constellation of avian flu strains (H5N1, H9N2, H7N7, etc), we continue to see rare sporadic human infections by reassorted swine viruses as well (Maine Confirms A 2nd trH3N2 Case).
Further evidence that nature’s laboratory is open 24/7, and that influenza viruses are constantly mutating and reassorting, looking for an evolutionary advantage.
While most of these reassortant viruses are doomed to end up in the evolutionary dustbin, failing to thrive and compete with other viruses, it only takes one fit, virulent, and easily transmissible virus to spark a global pandemic.
And that is something that might emerge tomorrow, next month, or perhaps not until years from now.
But history as history has us shown over and over:
Pandemics happen. Count on it.